1. Field of the Invention
The present invention relates to a biosensor and, more particularly, to a method and apparatus for measuring sample reaction results on a biosensor.
2. Description of Related Art
A biosensor has an electrode layer including a plurality of electrodes formed on an insulative substrate by screen printing or the like, and an enzyme reaction layer consisting of hydrophilic polymer, redox enzyme and electron acceptor on the electrode layer. When a sample containing a substrate is dropped on the enzyme reaction layer of the biosensor, the enzyme reaction layer is dissolved and the substrate and the enzyme are reacted with each other, thereby oxidizing the substrate and reducing the electron acceptor. A concentration of the substrate in the sample can be obtained from a current value obtained by electrochemically oxidizing the reduced electron acceptor after completion of the enzyme reaction.
A typical example of a biosensor acquiring a quantitative value of a specific ingredient of a bio-sample in an electrochemical manner is a sensor for blood sugar measurement. FIGS. 1 and 2 illustrate the sensor for blood sugar measurement.
FIG. 1 is an exploded perspective view of a typical biosensor except a reactive layer. FIG. 2 is a longitudinal sectional view of the biosensor shown in FIG. 1.
Referring to FIG. 1, leads 102 and 104 are formed by printing a silver paste on an insulative substrate 100. A working electrode 106 is formed by printing a conductive carbon paste containing a resin binder on the substrate 100. The working electrode 106 is connected to the lead 102. An insulation layer 108 is formed by printing an insulative paste on the substrate 100. The insulation layer 108 covers the periphery of working electrode 106, such that an exposed portion of the working electrode 106 maintains a fixed area. A ring-shaped counter electrode 110 is formed by printing the conductive carbon paste containing resin binder on the substrate 100 so as to be connected to the lead 104. A reactive layer is formed on or around an electrode layer consisting of the working electrode 106 and the counter electrode 110.
The substrate 100 having the reactive layer, a cover 114 having an air hole 112, and a spacer 116 are fixed to one another as shown in FIG. 1, thereby providing a biosensor. The spacer 116 has an insert hole 118 as a path for supplying a sample solution between the substrate 100 and the cover 114. A hydrophilic polymer layer 120, a reactive layer 122 including an enzyme and an electron acceptor, and a lecithin layer 124 are formed on the substrate 100 in this order.
When a bio-sample contacts an inlet 126 in the biosensor, the bio-sample is filled in the insert hole 118 by capillarity and, at the same time, air inside the insert hole 118 is discharged through the air hole 112 formed on the cover 114.
However, there is a problem in that since the air hole 112 is located over the sensor, a measurement error may occur due to contact with the air hole 112 when the sensor is used. Meanwhile, since the reaction begins to proceed at the moment when a sample contacts a reaction layer, the sample should be quickly absorbed irrespective of its viscosity. However, since the air hole 112 is located at the rear of sample path in the biosensor, it is difficult to quickly absorb the sample.
Since the biosensor includes three electrodes, detects whether or not the sample is fully injected, and makes a measurement, the above-mentioned absorption delay causes a measurement error in the biosensor.